Thermostat



June 25, 1935. E. H. PIRON THERMOSTAT Filed June 11, 1932 2 Sheets-Sheet 1 J0 Z6 E 47 2 PI 2p 24 28 30 31 FEEZQN THERMOSTAT Filed June 11, 1932 2 Sheets-Sheet 2 1 mas-($1 UNITED STATES PATENT OFFICE THERMOSTAT Emil H. Piron, Detroit,

Mich., assignor to The Detroit Edison Company, Detroit, Mich., a corporation of New York Application June 11, 1932, Serial No. 616,601

15 Claims.

This invention has to do with thermostats especially of the character employed in connection with domestic ranges and ovens, and has for its general object to provide a device of this character of improved construction.

Thermostats of this character heretofore in vogue have met with indifferent success because of complexity of construction necessitating a high cost of manufacture, low sensitivity, un-

reliability of operation, difiiculty of adjustment, fragility, and difficulty of replacement of parts.

It is accordingly the principal object of this invention to provide a thermostat involving few parts which may be produced by simple manufacturing operations, and, at the same time, a

thermostat which is reliable in operation, readily adjustable, rugged and durable, and which may be easily replaced.

It is a further object of this invention to provide an extremely simple means for calibrating a thermostat.

Another object of the invention is to provide a thermostat of the character mentioned which may be constructed at a very low cost.

A further object of the invention is to provide an improved toggle switch.

Further objects and advantages of the invention will appear as the description proceeds.

The invention contemplates generally the provision of a pivoted bar engageable on one side of its pivot by a temperature responsive element. This element projects into an electrically heated oven and is arranged to move the bar when the oven temperature is falling and to recede from the bar when the oven temperature is rising. A spring holds the bar in engagement with the element so that the bar follows the element as the latter recedes. The bar carries a toggle snap switch which controls the oven 40 heating circuit.

The frame of the device carries a temperature graduating dial with which a cam is associated. The cam is so arranged that it will trip the switch to open position when the oven temperature exceeds the temperature setting of the dial; Means are provided to urge the switch to, and yieldably hold the same in, closed position. The cam cooperates with the switch to prevent closing of the circuit by said means until the oven temperature falls below the temperature setting of the dial.

This invention (in a preferred form) is illustrated in the drawings and hereinafter more fully described.

On the drawings.

Figure 1 is a front elevational view of the device constructed in accordance with the prin- .ciples of the present invention.

Figure 2 is a sectional view taken approximately in the plane indicated by the line IIII 5 in Figure 1, a portion of the oven in conjunction with which the device is used being shown fragmentarily.

Figure 3 shows details of wiring employed in the invention.

Figure 4 is a diagrammatic view showing how the device operates.

Figure 5 is an enlarged fragmentary view of a detail of the invention.

Figure 6 is a fragmentary sectional view taken 15 approximately in the plane indicated by the line VI-VI in Figure 5.

Referring now more particularly to the drawings, wherein the same parts are designated throughout by the same referencecharacters, the apparatus includes a temperature responsive element comprising a metal rod l disposed in a metal tube 2, the 'rod being preferably of steel and the tube of brass, though any other suitable metals may be employed. An end of the rod is securely attached at 3, as by welding or the like, to an end of the tube and is telescoped therein, the parts being free from each other at their opposite ends 4 to expand and contract independently. The free end 5 of the tube 2 is fixed at i to a frame 7 and extends through an opening 8 into the interior of an electrically heated oven 9.

The frame 1 is disposed outside of the oven 9 and is secured to the latter by any suitable means such as the studs Ill. The frame 1, adjacent the as temperature responsive element, provides a knife edge pivot l I for a bar l2, said pivot being located near one end of the bar. The bar I! is provided adjacent and at one side of the pivot or fulcrum H with an adjustable bearing member [3 provided with a concave bearing surface I against which the rounded nose l5 of the free end of the rod l engages. The point or zone of engagement is so arranged with respect to the fulcrum H that during movement of the bar I2 about the fulcrum H, said point or zone is substantially coaxial with the rod I. A spring I6 is located between the frame I and the pivoted bar l2 near the end I! of the bar and on the opposite side of the fulcrum l l relative to the temperature responsive instrumentalities I and 2, whereby the bearing surface It is held yieldably in constant' engagement with the nose l5 of the rod I. Projections l8 and I9 located in the opposite ends of the spring l6 serve to hold the same in operative position.

The opposite end 20 of the pivoted bar or lever |2 carries a toggle switch indicated generally at 2| and comprising a base 22 of insulating material such as a phenolic condensation product and a bracket 23 providing ears 24 to which springs 25 are attached. Between the ears 24 is an opening 26 formed in a grooved portion 21. A blade 28 passes through the opening 26 and is provided. with shoulders 29- fitting in said grooved portion 21 and cooperating therewith to provide a substantially knife edge pivot for said blade.

A stud 30 has its shank secured at 3| to the base 22 and passes through the blade 28 adjacent the inner end 32 of the latter, the head of the shank being disposed on the outer side of the blade 28 and forminga stop limiting pivotal movement of the blade in one direction. Between the base 22 and the blade 28 and surrounding the shank of the stud 30 is a spring 30*- which urges the blade outward toward the head of the stud.

Also included in the toggle mechanism is a second blade 33 of substantially T-shape, the shank 34 being formed at its outer end with a socket 35 in which the inner end 32 of the first blade 28 is received, thereby providing a substantially knife edge pivot between the blades. The head 36 of the blade 33 receives the other ends of the springs 25 at 31 and is yieldably urged by said springs toward the first blade 28, whereby the inner end 32 of the blade 28 is held in the socket 35 0f the blade 33. The springs 25 thereby operate to snap the second blade 33 on one side or the other of dead center, that is, the plane of the blade 28.

The inner end 38 of the blade 33 is arranged to be yieldably held by the springs 25 in engagement with the contact point 39 of an electric circuit employed in heating the oven 9, said contact being electrically connected as shown at 40 in Figure 3 to a binding post 4|. The bracket 23 is electrically connected at 42 through the bus bar 43 to a second binding post 44, all such metal portions being insulated by the strip 45 from the bar |2. A bracket 46 secured to the base 22 overlies the inner end 38 of the blade 33 and serves to limit. movement of said blade when snapped over dead center on the opposite side to that shown in Figure 2.

The frame I is provided adjacent the toggle mechanism with an offset portion 41 which rotatably carries a dial 48 suitably graduated preferably in degrees Fahrenheit as shown at 49. Secured to the dial 48 for rotation therewith is a cam 50. The cam 50 is so arranged with respect to the graduations on the dial 48, that the high part of the cam is located in the path of movement of the tail end 5| of the blade 28 when the dial is set for a low temperature for the oven or furnace, and the low part of the cam is in the path of movement of said end 5| when the dial is set for a high temperature.

The operation of the foregoing mechanism is as follows:

Let us assume that the oven 9 is cold and that the dial 48 is set at 450 F., which is the setting shown on the drawings. A switch 53, employed in connection with this mechanism, is turn-ed on and electric current allowed to pass through the line going to the resistance coils 54 of the oven heater. The blade 33 and contact 31 are connected in series in said line and the temperature responsive rod-tube element, 2, is in the oven. As the temperature in the oven 9 rises, the tube 2 expands more than the rod I so that the nose |5 of mences to cool.

the rod recedes from the lever 2. Due to the action of the spring Hi, the lever or pivoted bar |2 turns about the fulcrum H as a pivot and follows the recession of the rod moving in the direction indicated by the arrow A. The parts may be initially so calibrated that when the current is first turned on, the tail end 5| of the blade 28 is either out of contact with the cam 5|] or in contact with the cam as shown in Figure 2. In either event, as the lever |2 continues to move, the tail end 5| of the blade 28 is arrested by the cam 50, the blade 28 thereafter being forced by the bracket 23 and against the action of the springs 25 and 3|] to pivot about said bracket and also about the cam 50 at its point of contact therewith. As a result of this movement, the angle between the blades 28 and 33 approaches 180, and with the continuing movement of the lever |2 the springs 25 snap the blades over to the other side of dead center so that they occupy the positions shown in dotted lines in Figure 4.

As a result of this action, the blade 33 is separated from the contact 39, thereby opening the oven heater circuit, whereupon the oven 9 com- The device is so calibrated that the blades 28 and 33 are snapped to the positions shown in dotted lines in Figure 4 when the temperature of the oven 9 is 450 F. The adjustable bearing |3 provides an extremely simple means for calibrating the device so that the circuit will be opened when the temperature of the oven 9 reaches the desired figure on the dial 48. That is, by adjusting the bearing Hi to the right as shown in Figures 2 and 4, the lever l2 will initially occupy a position counterclockwise of that shown in these figures, so that a greater amount of expansion of the temperature responsive element 2, will be necessary to effect an opening of the make and break device 2|, and by adjusting the bearing |3 to the left, a lower oven temperature will serve to snap said make and break device.

As the oven 9 cools, the contraction of the tube 2 being greater than that of the rod the nose |5 of the rod is forced against the bearing |3, thereby swinging the lever |2 in a direction opposite to that indicated by the arrow A, until the blades 28 and 33 are again snapped to their full line positions as shown in Figures 2 and 4. The blade 33 is thereby brought into contact with the contact point 39 and closes the oven heater circuit, whereupon the temperature of the oven commences to rise and the same cycle continually ensues.

It will be observed that in actual practice the blades 28 and 33, whether arranged on one or the other side of dead center, are disposed at an angle within a few degrees of a straight angle, and that the rod engages the lever |2 at a point which is much closer to the fulcrum than the toggle mechanism. Thus only a very slight movement of the rod one'way or the other is sufficient to operate the oven heater circuit switch. The mechanism is therefore extremely sensitive and will serve to maintain the temperature of the oven substantially constant for all practical purposes.

From the foregoing, it will be seen that in accordance with the present invention, a minimumof movable parts is employed, and in fact the entire construction requires few parts. all of which may be made by simple molding, stamping and screw machine operations. The construction is very neat and compact, occupies very little space, may be assembled readily, will not get out of order and is capable of easy adjustment and replacement.

It will be observed that the spring 30* urges the blade 33 into engagement with the contact 39 and that the pressure of said spring is overcome by the cam 50 when the temperature of the oven reaches the limiting temperature, by reason of the pivotal action imparted to the blade 28 by the cam 50 while the oven temperature is increasing. The inner part of the blade 28, during its pivotal movement, approaches the base 22 and compresses the spring 30. As the oven temperature falls, the inner part of the blade 28 is moved by the bar 12 bodily away from the cam, and the spring 30 causes the blade to pivot in the opposite direction until the limiting temperature of the oven is reached. It will be appreciated that while the spring 30 is arranged to urge the switch into closed position and thecam 50 operates to open the switch, these parts could very easily be arranged to have the opposite effects on the switch.

The knife edge pivot at 35 between the blades 28, 33 is such as to prevent relative sidewise movement of said blades. To this end, the blade 33 at the pivot 35 is provided with a tongue 35**, and the adjacent end of the blade 28 is provided with a slot 28 in which the tongue 35 is received as shown in Figures and 6.

The mounting of the dial 48 and cam 50 is such that the same are frictionally held in the position to which the same are rotated. In practice, a stationary index line is provided for cooperation with the graduations on the dial 48. If

desired, a movable pointer and stationary dial could be employed.

It will be noted that the base 22 is rabbeted at 22* and is provided with attaching screws 52 to receive a housing (not shown) for the switch mechanism.

The wiring diagram appearing in Figure 4 in conjunction with the diagrammatic showing of the construction embodying the invention shows the toggle switch 2| in series with a hand switch 53 and the oven heating element 54.

I am aware that many changes may be made and numerous details of construction may be varied through a wide range without departing from the principles of this invention, and I therefore do not purpose limiting the patent granted hereon otherwise than necessitated by the prior art.

I claim as my invention:

1. In a. device of the class described, a frame, a lever pivotally connected near one end to said frame, a temperature responsive element engaging said lever adjacent and on one side of the pivot, means for yieldably holding said element in engagement with said lever, a toggle make and break device including a pair of relatively separable contacts carried by the other end of the lever and movable therewith, and means for arresting movement of one end of said make and break device during pivotal movement of said lever in one direction.

2. In a thermostat, a frame, a lever carried thereby, a temperature responsive element for actuating said lever in one direction, a spring for causing said lever to follow said element in the other direction, and means controlled by by said lever for controlling said element, said means comprising a plurality of relatively separable contacts forming a switch carried bodily by the lever, and a stationary trip for. said switch.

3. In a thermostat, a switch including a movable contact and a relatively fixed contact, yieldable means associated with said switch and constantly urging said movable contact into engagement with the other contact, a movable member bodily carrying said switch and means, a trip element disposed in the path of movement of the switch during movement of said member and acting in opposition to the yieldable means, a spring constantly urging said member toward said element, and a temperature responsive device for moving said member away from said element.

4. In a thermostat, a switch including a movable contact and a relatively fixed contact, yieldable means associated with said switch and constantly urging said movable contact into engagement with the other contact, a movable member bodily carrying said switch and means, a trip element disposed in the path of movement of the switch during movement of said member and acting in opposition to the yieldable means, a spring constantly urging said member toward said element, a temperature responsive device for moving said member away from said element, and means for snapping said movable contact into and out of engagement with the fixed contact.

5. In a thermostat, a switch including a movable contact and a relatively fixed contact, yieldable means associated with said switch and constantly urging said movable contact into engagement with the other contact, a movable member bodily carrying said switch and means, a trip element disposed in the path of movement of the switch during movement of said member and acting in opposition to the yieldable means, a spring constantly urging said member toward said element, a temperature responsive device for moving said member away from said element, and means for varying the length of stroke of said member.

6. In a thermostat, a switch including a movable contact and a relatively fixed contact, yieldable means associated with said switch and constantly urging said movable contact into engagement with the other contact, a movable member bodily carrying said switch and means, a trip element disposed in the path of movement of the switch during movement of said member and acting in opposition to the yieldable means,

a spring constantly urging said member toward said element, a temperature responsive device for moving said member away from said element, and means for changing the position of said element to vary the time of tripping of the movable contact to open position.

'7. In a thermostat, a frame, a movable memher, a. temperature responsive element, means for causing said member to move with said element in opposite directions, a trip switch carried by said member and including a blade, means yieldably urging said blade to closed position, and a cam located in the path of movement of said blade when said element expands whereby to trip said blade into open position, said cam being rotatably mounted to vary its distance from said blade so that the switch may be operated upon different movements of said member.

8. A switch comprising a support, a bracket carried by said support, a lever pivoted between its ends to and extending beyond said bracket, a movable contact having one end pivoted to the inner end of said lever, spring means connected to and tensioned between the bracket and said contact on opposite sides of the second pivot for snapping said lever and contact beyond dead center in both directions with respect to the second pivot, a spring engaging said lever and constantly urging said lever and contact in one direction beyond dead center, a fixed contact carried by said support and engageable by the movable contact to close an electric circuit when the movable contact is disposed on one side of dead center, means including a temperature responsive element for moving said support, and a device engageable with the other end of said lever upon movement of said support in one direction for tripping the lever and movable contact in opposition to said spring.

9. A switch comprising a support, a lever pivoted between its ends to said support, a movable contact having one end pivoted to the inner end of said lever, spring means connected to and tensioned between said support and said contact on opposite sides of the second pivot for snapping the lever and contact beyond dead center in both directions with respect to the second pivot, a spring engaging said lever and constantly urging the same and said contact toward one side of dead center, a fixed contact carried by said support and engageable by said movable contact to close an electric circuit when the movable contact is disposed on one side of dead center, means including a temperature responsive element for moving said support, and a device engageable with the other end of said lever upon movement of said support in one direction for tripping said lever and movable contact in opposition to said pring.

10. A switch comprising a support, a lever pivoted between its ends to said support, a movable contact having one end pivoted to the inner end of said lever, spring means connected to and tensioned between said support and said contact on opposite sides of the second pivot for snapping the lever and contact beyond dead center in both directions with respect to the second pivot, a spring engaging said lever and constantly urging the same and said contact in one direction beyond dead center, a fixed contact carried by said support and engageable by said movable contact to close an electric circuit when the movable contact is disposed on one side of dead center, means including a temperature responsive element for moving said support, a device engageable with the other end of said lever upon movement of said support in one direction for tripping said lever and movable contact in opposition to said spring, and means for varying the distance between said device and the second end of said lever so that said switch may be operated upon different movements of said support.

11. A switch comprising a support, a lever pivoted between its ends to said support, a movable contact having one end pivoted to the inner end of said lever, spring means connected to and tensioned between said support and said contact on opposite sides of the second pivot for snapping the lever and contact beyond dead center in both directions with respect to the second pivot, a spring engaging said lever and constantly urging the same and said contact in one direction beyond dead center, a fixed contact carried by said support and engageable by said movable contact to close an electric circuit when the movable contact is disposed on one side of dead center, means including a temperature responsive element for moving said support, and a device engageable with the other end of said lever upon movement of said support in one direction for tripping said lever and movable contact in opposition to said spring, said device comprising a rotary dial graduated in degrees of temperature, and a cam r0- tatable with said dial and arranged with its high part adjacent the second end of the lever when the dial is set for low temperature, and remote from said second end when the dial is set for high temperature.

12. A switch comprising a support, a lever pivoted between its ends to said support, a movable contact having one end pivoted to the inner end of said lever, spring means connected to and tensioned between said support and said contact on opposite sides of the second pivot for snapping the lever and contact beyond dead center in both directions with respect to the second pivot, a spring engaging said lever and constantly urging the same and said contact in one direction beyond dead center, a fixed contact carried by said support and engageable by said movable contact to close an electric circuit when the movable contact is disposed on one side of dead center, means including a temperature responsive element for moving said support, and a device engageable with the other end of said lever upon movement of said support in one direction for tripping said lever and movable contact in opposition to said spring, said last means including a spring for moving said support in a direction opposite to that in which the support is moved by the temperature responsive element.

13. A thermostat comprising a switch mounted for bodily movement and having cooperable and relatively separable contacts adapted to open and close an electric circuit, temperature responsive means operable to bodily move said switch and contacts as a unit, a switch actuating member, and a trip element disposed in the path of travel of said member and engaged thereby during movement of the switch.

14. A thermostat comprising a switch mounted for bodily movement and having cooperable and relatively separable contacts adapted to open and close an electric circuit, temperature responsive ,means operable to bodily move said switch and contacts as a unit, a switch actuating member, and a trip element disposed in the path of travel of said member and engaged thereby during movement of the switch, said element being adjustable to cause said engagement to occur at different relative positions of the switch.

15. A thermostatic control device including a pair of relatively separable contacts forming a switch mounted for bodily movement, temperature responsive means operable to bodily move said switch, a contact operating member, and a trip element disposed in the path of travel of said member and engaged thereby during movement of the switch.

. EMIL H. PIRON. 

